As it is well known in the field of aircraft engine technology, with the advent of high performance gas turbine engines and the emphasis placed on economy, it is the goal of the engine designer to not only improve the performance of the engine, but to also reduce the capital and operational costs relating thereto. Obviously, loss of pressure of the engine's working medium either contributes to degradation in engine performance or requires that the designer increase the overall pressure to achieve the design performance. This results in a sacrifice to the overall weight and economics of the engine.
One area of concern has been with the performance of the augmentor. Obviously when the augmentor is not being utilized, which can be for a significant portion of the aircraft's mission, and it is in the quiescent state, the augmentor's fuel spray bars and flame holders have added to the pressure loss of the engine. Hence, the components of the augmentor that are in the gas path or main flow stream incur a dry pressure loss and in this state contribute nothing in terms of engine's performance. The pressure loss that occurs during the period when the augmentor is not activated is referred to as "dry pressure loss".
State-of-the-art heretofore known augmentor designs utilize bluff body flame stabilization techniques to anchor the combustion process within the augmentor. The flameholding system generally consists of a full circumferential "V-gutter" pilot that ensures flame propagation to the remaining elements of the system. A multitude of radial "V-gutters" emanating from the pilot gutter toward both the chamber wall and the augmentor's center line act to spread the flame over the entire cross-section of the flow path.
As one skilled in this art will appreciate, in order to achieve proper flame stability, the width of the bluff bodies are typically on the order of 0.75 to 2.0 inches depending on the conditions under which the augmentor must operate. Because the combustion efficiency of the augmentor is dependent on the number of bluff body stabilizers used, the designer is confronted with a compromise between operability, combustion efficiency and/or the length of the augmentor in order to attain a viable design. Obviously, no matter what selections result from these trade-offs, owing to the bluff bodies the consequence of this design will adversely affect the pressure of the gas path. As is well known, the current dry pressure loss in the augmentor incidental to current design practices range between 1.5 to 3.0%.
The present invention contemplates a new augmentor burner design that will achieve extremely low dry pressure loss while maintaining excellent or that which is at least equal to heretofore known augmentor's combustion performance and operability. In accordance with this invention, the heretofore known bluff bodies are eliminated from the augmentor and the fuel spray bars are integrated into aerodynamically shaped struts or vanes typically associated with the turbine exhaust case.